A loading-port unit is for conveying many wafers contained in a wafer carrier placed thereon to a semiconductor-device manufacturing unit.
As shown in FIG. 36, many wafers U are contained in a wafer carrier C, which is placed on a unit body 201 of a loading-port unit L. Each of the wafers U is adapted to be conveyed into a semiconductor-device manufacturing unit H by means of a robot unit 291. The loading-port unit L is provided with an attaching and removing unit for attaching and removing a lid 206 of the wafer carrier C. In FIG. 36, 292 represents a clean-air supplying unit, which is for supplying clean air into the semiconductor-device manufacturing unit H.
As an example of the attaching and removing unit of the lid 206, there is a structure shown in FIG. 37. In such a case of the attaching and removing unit 200, key elements 221 provided on a lid holding plate 215 are fitted into keyholes 222 of lock units E provided at the lid 206 of the wafer carrier C. Then, if the key elements 221 are pivoted in a predetermined direction, the lid 206 is locked or unlocked with respect to the wafer carrier C. When the lock units E of the lid 206 are unlocked, the lid 206 and the lid holding plate 215 are engaged with each other. In that state, the lid holding plate 215 is caused to move in a horizontal direction perpendicular to the lid 206. Thus, the lid 206 of the wafer carrier C is caused to move in the same direction while held by the lid holding plate 215, and hence removed from the wafer carrier C.
However, there may be a case wherein the lid 206 is not held by the lid holding plate 215, even if the attaching and removing unit 200 operates. For example, if a main part 221a (a part for being engaged with the keyhole 222) of the key element 221 is broken off, the key element 221 is pivoted only in vain even if the key element 221 is pivoted with it fitted into the keyhole 222, so that the lock unit E is never unlocked. In addition, similar is the case wherein a protrusion 218b of a disk plate 218, which forms the lock unit E, is broken off. In this case, the lid 206 remains attached to the wafer carrier C. If an arm (not shown) of the robot unit 291 is going to move into the wafer carrier C in order to convey the wafer U in the above state, the arm may interfere with the lid 206.
While the lid 206 is held by the lid holding plate 215 and temporarily put in a lower part of the loading-port unit L, if electric power supply is stopped because of a power failure or the like and then restarted, each key element 221 is returned to a starting-point thereof (to a lateral attitude thereof in this case). In the case, the engagement between the main part 221a of the key element 221 and the keyhole 222 of the lock unit E is released, and then the key element 221 is in a condition only inserted into the keyhole 222. Thus, there is a possibility that the lid 206 may fall.